A laser of this type has been known from DE-OS 3,339,370. The conventional laser emits a pulsed, polarized laser beam, the intensity of which is varied by adjustment of a polarizing cube with an operating knob. After release of the operating knob, a testing pulse is triggered, the energy of this pulse is measured and optionally readjusted. Instead of adjusting the polarizing cube, it is also possible to change the voltage of the laser flash lamp.